In the prior art, heat treatment of a semiconductor substrate (wafer) as a workpiece is conducted in a testing step for a semiconductor. In other words, the wafer is heated to a higher temperature than the usual usage temperature, and any semiconductor chips which have the possibility of failing are made to fail at an accelerated rate and are removed. This is a burn-in test in order to prevent the occurrence of failure after shipping. In the burn-in step, after forming a semiconductor circuit on the semiconductor wafer and prior to cutting the individual chips, the electrical performance of each chip is measured while the wafer is being heated. Any defective products are removed. With this burn-in step, there is a strong desire to shorten the processing time in order to improve the through-put.
In addition, after the chips are individually cut and enclosed in a packaging or the like, the semiconductor is similarly heated, and the electrical performance is measured, and defective products are removed. When running electricity through the chips and measuring the electrical properties, the chip generates heat. In recent years, chips have increased in their outputs, with some at 100 W or greater. The chips can be destroyed by their own heat. As a result, after measuring the electrical properties, rapid cooling is necessary.
With this burn-in step, a heater is used for holding the semiconductor substrate and for heating the semiconductor substrate. In the heater of the prior art, the entire undersurface of the wafer must be in contact with the ground electrode, and as a result, metal heaters are used. A wafer on which a circuit is formed is placed on top of a flat, metal heater, and the electrical properties of the chip are measured. During measurement, a measuring device called a probe card, which has a plurality of electrode pins for forming an electrical connection, is pressed against the wafer at a force of several 10's of kgf to several hundred kgf. If the heater is thin, the heater can become deformed, and there may be contact failure between the wafer and the ground electrode. As a result, in order to maintain the rigidity of the heater, a thick metal plate of thickness 15 mm or greater must be used. Raising and lowering the temperature of the heater requires a long time, and this has become a major obstacle in improving throughput.
In Japanese Laid Open Patent Publication Number 2001-033484, a wafer prober is proposed, in which instead of a thick metal plate, a thin metal layer is formed on the surface of a ceramic substrate. Even though it is thin, the ceramic substrate has high rigidity and does not deform readily. As a result, this wafer prober does not readily deform and has a small thermal capacity. According to Japanese Laid Open Patent Publication Number 2001-033484, because of the high rigidity, contact failure does not occur, and because the thermal capacity is small, the temperature is raised and lowered in a short amount of time.
With the burn-in step, the measurement temperature will be different depending on the use of the chip. As an example, electrical properties are measured at a maximum temperature of 200 degrees C. and a minimum temperature of −35 degrees C. Of the multiple chips formed on a wafer, only the chip that is going to have its electrical properties measured needs to be heated to 200 degrees C. However, with the heater of the prior art, such as in Japanese Laid Open Patent Number 2001-033484, the entire wafer is heated, and all of the chips formed on the wafer are heated.
When a chip is exposed to high temperatures for a long period of time, there can be deterioration of properties due to the heat. Preferably, chips that are not being measured do not have their temperatures raised, and only the chip being measured has its temperature raised to the measurement temperature. However, with the heater of the prior art described above, when a plurality of 20 mm square chips are formed on wafers of diameter 200 mm or 300 mm, it is difficult to raise the temperature of a single chip independently. In addition, with the self-generated heat as describe above, not only is that chip damaged, but the surrounding chips may be damaged as well.